CORBA Vs. DCOM
The CORBA standard is defined by an international body of companies and research institutes, and is an open standard. DCOM is a proprietary standard developed by Microsoft, but is much more widely used because of its advanced state, and strong support in their OSes and development tools.
CORBA is inter-operable to many platforms and programming languages (including various real-time operating systems). DCOM is implemented in Microsoft's OSes, and is being ported to other platforms, by companies such as Mainsoft. DCOM is supported by many programming languages as well.
It is said that CORBA is more scalable because it does not perform constant keep-alive message delivery as DCOM does.